The present invention relates to a multiplex system in a vehicle, and more particularly, to a power and communications network in a vehicle that is fault tolerant and immune to single point failure.
An area in the auto industry seeing tremendous change from past practices is the area of wiring and interconnects. The creation of relatively inexpensive microprocessors, and the digital revolution, have put the power of the computer into the hands of automotive engineers. Traditionally large bundles of wires were used to conventionally connect electrical devices in automobiles, each wire representing a single switching signal or analog value. These bundles of wires increased the weight, volume, and complexity of a vehicle. With the advent of automotive computer multiplexing networks such as the controller area network (xe2x80x9cCANxe2x80x9d), Palmnet, Chrysler Collision Detection (xe2x80x9cCCDxe2x80x9d), and SAE J1850, many of these wires and their associated terminations and connectors can be eliminated. Large amounts of information can now be transferred between intelligent control devices in an automobile via a single wire.
Conventional multiplex applications utilizing single wire communication for control devices and instrumentation are vulnerable to single point failure in their communications wire. For example, if the communications wire were shorted or disconnected, the remotely located controls would for all practical purposes, be useless as they would not be able to receive or transmit information. This is an undesirable result for most consumers since they will lose the functionality of certain controls until they repair the vehicle. Accordingly, there is a need in the art to provide for a communications backup in the event of a fault in the communications wire between a remotely located and controlled device and the control infrastructure of a vehicle.
According to one aspect of the present invention, a primary or master node communicates via a standard multiplex protocol, such as those previously cited, to the control infrastructure of a vehicle. The master node, in a subnetwork or supplementary communications bus, further communicates with one or a plurality of slave nodes in a local vehicle area or structure such as a seat. The main multiplex network and subnetwork are bridged by the master node which transfers information between the main multiplex network and the subnetwork. By localizing at least a portion of the networking in the vehicle, the main multiplex network functions generally substantially independent of the subnetwork operation.
The master node in the subnetwork communicates over a first primary communications bus/wire to the slave nodes and transfers power via a secondary power bus/wire to the slave nodes. Accordingly, two wires using vehicle ground as a common reference connect the master node to a slave node to transfer communications and power. In alternate embodiments, an additional common reference wire may be provided. In the case of multiple slave nodes, wires may be daisy-chained from slave node to slave node to allow communications and power transfer from the master node.
In some situations, the primary communications bus/wire may be shorted or pulled high, preventing communication between the master node and the remotely located slave nodes, disabling the remote controls and actuators. In such a situation where the remote slave node is a seat adjusting motor or a window control switch, the seat and window will be inoperable. This result is unacceptable for most consumers since they expect to be able to adjust such devices in their vehicles regardless of faults in a vehicle. In the event of a failure in the primary communications bus/wire, the present invention will transmit information over the secondary power bus/wire.
In the present invention, the secondary power bus/wire has the capability to be used as a redundant communications bus between the master node and slave nodes. In the preferred embodiment, the data transmission over the secondary power bus/wire will be half duplex with only the master transmitting control commands to the slave node. In alternate embodiments, the transmission will be full duplex with the master sending commands to the slave and the slave sending commands and status information to the master node. In this manner, the subnetwork will be able to survive a failure in the primary communications bus/wire and enable a vehicle operator to fully operate the controls of the vehicle until the problem is fixed.